Hi birdies, I'd like to disregard an (in the literal sense) expensive OSPF path. The preferred path is longer in terms of OSPF. All nodes in the network are running BIRD2 and are in our management so we're in full control. What would be the most elegant approach to do this? Thanks! Best regards, Kees -- https://nefos.nl/contact Nefos IT bv Ambachtsweg 25 (industrienummer 4217) 5627 BZ Eindhoven Nederland KvK 66494931 /Aanwezig op maandag, dinsdag, woensdag en vrijdag/
Hi, On 14.02.20 22:03, Kees Meijs wrote:
I'd like to disregard an (in the literal sense) expensive OSPF path. The preferred path is longer in terms of OSPF.
Does it have a larger cost than the one you want to avoid? Why not increase its cost? Regards -- Robert Sander Heinlein Support GmbH Schwedter Str. 8/9b, 10119 Berlin https://www.heinlein-support.de Tel: 030 / 405051-43 Fax: 030 / 405051-19 Amtsgericht Berlin-Charlottenburg - HRB 93818 B Geschäftsführer: Peer Heinlein - Sitz: Berlin
Hi Robert, The path I'm trying to avoid has the lowest OSPF cost but in the physical world the most... :-) I'll fiddle for a bit with OSPF cost. Seems a clean solution. Thanks! Regards, Kees On 17-02-2020 08:57, Robert Sander wrote:
Does it have a larger cost than the one you want to avoid? Why not increase its cost?
Hi, On 17.02.20 09:03, Kees Meijs wrote:
The path I'm trying to avoid has the lowest OSPF cost but in the physical world the most... :-)
I always thought the OSPF cost represents the "physical" cost of a link. Regards -- Robert Sander Heinlein Support GmbH Schwedter Str. 8/9b, 10119 Berlin https://www.heinlein-support.de Tel: 030 / 405051-43 Fax: 030 / 405051-19 Amtsgericht Berlin-Charlottenburg - HRB 93818 B Geschäftsführer: Peer Heinlein - Sitz: Berlin
Robert, Robert Sander wrote:
On 17.02.20 09:03, Kees Meijs wrote:
The path I'm trying to avoid has the lowest OSPF cost but in the physical world the most... :-) I always thought the OSPF cost represents the "physical" cost of a link.
Not necessarily. From RFC 2328, p. 18 [0]:
A cost is associated with the output side of each router interface. This cost is configurable by the system administrator. The lower the cost, the more likely the interface is to be used to forward data traffic. Costs are also associated with the externally derived routing data (e.g., the BGP-learned routes).
From RFC 2328, p. 66 [0]:
Interface output cost(s) The cost of sending a data packet on the interface, expressed in the link state metric. This is advertised as the link cost for this interface in the router-LSA. The cost of an interface must be greater than zero.
In essence. The interface metric used by OSPF is just an arbitrarily decided value. With every Network Operating System having some built-in values used [3]. But as well, often available to be re-configured by the Systems/Network Administrator if the Network design of choice requires so. Footnotes: ------------------------------------------------------------ [0]: https://www.rfc-archive.org/getrfc?rfc=2328 [1]: https://packetlife.net/media/library/10/OSPF.pdf [2]: https://packetlife.net/media/library/40/IOS_Interior_Routing_Protocols.pdf [3]: https://www.omnisecu.com/cisco-certified-network-associate-ccna/what-is-ospf... [4]: http://docs.frrouting.org/en/latest/ospfd.html#configuring-ospf [5]: http://docs.frrouting.org/en/latest/ospf6d.html#ospf6-router [6]: https://unix.stackexchange.com/questions/381905/ospf-route-costs-in-bird [7]: https://gitlab.labs.nic.cz/labs/bird/wikis/OSPF_example -- Best regards, Chriztoffer
On Mon, Feb 17, 2020 at 01:22:22PM +0100, Robert Sander wrote:
Hi,
On 17.02.20 09:03, Kees Meijs wrote:
The path I'm trying to avoid has the lowest OSPF cost but in the physical world the most... :-)
I always thought the OSPF cost represents the "physical" cost of a link.
Hi There is no such think as 'physical' cost of a link. Cost is always an administrative property. There are several physical properties of a link (like latency, throughput, technology) and it is a question of policy how to convert them to OSPF cost. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."
On 17.02.20 16:37, Ondrej Zajicek wrote:
There is no such think as 'physical' cost of a link. Cost is always an administrative property. There are several physical properties of a link (like latency, throughput, technology) and it is a question of policy how to convert them to OSPF cost.
Yes, you are right. I just summarized all that under "physical" cost. In the end the OSPF cost is an arbitrary value set by the router admin. Regards -- Robert Sander Heinlein Support GmbH Schwedter Str. 8/9b, 10119 Berlin https://www.heinlein-support.de Tel: 030 / 405051-43 Fax: 030 / 405051-19 Amtsgericht Berlin-Charlottenburg - HRB 93818 B Geschäftsführer: Peer Heinlein - Sitz: Berlin
participants (4)
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Chriztoffer Hansen -
Kees Meijs -
Ondrej Zajicek -
Robert Sander